BCM4319 Preliminary Data Sheet
MAC Features
The TXE module also contains the hardware that allows the rapid assembly of MPDUs into an A-MPDU for
transmission. The hardware module aggregates the encrypted MPDUs by adding appropriate headers and pad
delimiters as needed.
RXE
The RXE constitutes the receive data path of the MAC. It interfaces with the DMA engine to drain the received
frames from the RXFIFO. It transfers bytes across the MAC-PHY interface and interfaces with the WSE module
to decrypt frames. The decrypted data is stored in the RXFIFO.
The RXE module contains programmable filters that are programmed by the PSM to accept or filter frames
based on several criteria such as receiver address, BSSID, and certain frame types.
The RXE module also contains the hardware required to detect A-MPDUs, parse the headers of the containers,
and disaggregate them into component MPDUS.
IFS
The IFS module contains the timers required to determine interframe space timing including RIFS timing. It also
contains multiple backoff engines required to support prioritized access to the medium as specified by WMM.
The interframe spacing timers are triggered by the cessation of channel activity on the medium as indicated by
the PHY. These timers provide precise timing to the TXE to begin frame transmission. The TXE uses this
information to send response frames or perform transmit frame bursting (RIFS or SIFS separated, as within a
TXOP).
The backoff engines (for each access category) monitor channel activity in each slot duration to determine
whether to continue or pause the backoff counters. When the backoff counters reach 0, the TXE gets notified
so that it may commence frame transmission. In the event that multiple backoff counters decrement to 0 at the
same time, the hardware resolves the conflict based on policies provided by the PSM.
The IFS module also incorporates hardware that allows the MAC to enter a low-power state when operating
under the IEEE power-save mode. In this mode, the MAC is in a suspended state with its clock turned off. A
sleep timer, whose count value is initialized by the PSM, runs on a slow clock and determines the duration over
which the MAC remains in this suspended state. The MAC is restored to its functional state when the timer
expires. The PSM updates the TSF timer based on the sleep duration, ensuring that the TSF is synchronized
to the network.
The IFS module also contains the PTA hardware that assists the PSM in Bluetooth coexistence functions.
TSF
The TSF module maintains the TSF timer of the MAC. It also maintains the target beacon transmission time
(TBTT). The TSF timer hardware, under the control of the PSM, is capable of adopting timestamps received
from beacon and probe response frames in order to maintain synchronization with the network.
The TSF module also generates trigger signals for events that are specified as offsets from the TSF timer, such
as uplink and downlink transmission times used in PSMP.
Broadcom®
Single-Chip IEEE 802.11™ a/b/g/n MAC/Baseband/Radio
Page 38
April 2, 2014 • 4319-DS05-R
CYPRESS [ CYPRESS ]
